Heat shock proteins were originally observed to be expressed in increased amounts in mammalian cells which were exposed to sudden elevations of temperature, while the expression of most cellular proteins is significantly reduced. It has since been determined that such proteins are produced in response to various types of stress, including glucose deprivation. As used herein, the term “heat shock protein” will be used to encompass both proteins that are expressly labeled as such as well as other stress proteins, including homologs of such proteins that are expressed constitutively (i.e., in the absence of stressful conditions). Examples of heat shock proteins include BiP (also referred to as grp78), hsp/hsc70, gp96 (grp94), hsp60, hsp40 and hsp90.
Heat shock proteins have the ability to bind other proteins in their non-native states, and in particular to bind nascent peptides emerging from ribosomes or extruded into the endoplasmic reticulum. Hendrick and Hartl., Ann. Rev. Biochem. 62:349-384 (1993); Hartl., Nature 381:571-580 (1996). Further, heat shock proteins have been shown to play an important role in the proper folding and assembly of proteins in the cytosol, endoplasmic reticulum and mitochondria; in view of this function, they are referred to as “molecular chaperones”. Frydman et al., Nature 370: 111-117 (1994); Hendrick and Hartl., Ann. Rev. Biochem. 62:349-384 (1993); Hartl, Nature 381:571-580 (1996).
For example, the protein BiP, a member of a class of heat shock proteins referred to as the hsp70 family, has been found to bind to newly synthesized, unfolded p immunoglobulin heavy chain prior to its assembly with light chain in the endoplasmic reticulum. Hendershot et al., J. Cell Biol. 104:761-767 (1987). Another heat shock protein, gp96, is a member of the hsp90 family of stress proteins which localize in the endoplasmic reticulum. Li and Srivastava, EMBO J. 12:3143-3151 (1993); Mazzarella and Green, J. Biol. Chem. 262:8875-8883 (1987). It has been proposed that gp96 may assist in the assembly of multi-subunit proteins in the endoplasmic reticulum. Wiech et al., Nature 358:169-170 (1992).
It has been observed that heat shock proteins prepared from tumors in experimental animals were able to induce immune responses in a tumor-specific manner; that is to say, heat shock protein purified from a particular tumor could induce an immune response in an experimental animal which would inhibit the growth of the same tumor, but not other tumors. Srivastava and Maki, 1991, Curr. Topics Microbial. 167:109-123 (1991). The source of the tumor-specific immunogenicity has not been confirmed. Genes encoding heat shock proteins have not been found to exhibit tumor-specific DNA polymorphism. Srivastava and Udono, Curr. Opin. Immunol. 6:728-732 (1994). High resolution gel electrophoresis has indicated that gp96 may be heterogeneous at the molecular level. Feldweg and Srivastava, Int. J. Cancer 63: 310-314 (1995). Evidence suggests that the source of heterogeneity may be populations of small peptides adherent to the heat shock protein, which may number in the hundreds. Id. It has been proposed that a wide diversity of peptides adherent to tumor-synthesized heat shock proteins may render such proteins capable of eliciting an immune response in subjects having diverse HLA phenotypes, in contrast to more traditional immunogens which may be somewhat HLA-restricted in their efficacy. Id.
Recently, Nieland et al. (Proc. Natl. Acad. Sci. U.S.A. 93:6135-6139 (1996)) identified an antigenic peptide containing a cytotoxic T lymphocyte (CTL) vesicular stomatitis virus (VSV) epitope bound to gp96 produced by VSV-infected cells. Neiland's methods precluded the identification of any additional peptides or other compounds which may also have bound to gp96, and were therefore unable to further characterize higher molecular weight material which was bound to gp96 and detected by high pressure liquid chromatography.
It has been reported that a synthetic peptide comprising multiple iterations of NANP (Asp Ala Asp Pro) malarial antigen, chemically cross-linked to glutaraldehyde-fixed mycobacterial hsp65 or hsp70, was capable of inducing antibody formation (i.e., a humoral response) in mice in the absence of any added adjuvant; a similar effect was observed using heat shock protein from the bacterium Escherichia coli. Del Guidice, Experientia 50:1061-1066 (1994); Barrios et al., Clin. Exp. Immunol. 98:224-228 (1994); Barrios et al., Eur. J. Immunol. 22:1365-1372 (1992). Cross-linking of synthetic peptide to heat shock protein and possibly glutaraldehyde fixation was required for antibody induction. Barrios et al., Clin. Exp. Immunol. 98:229-233.
It has now been discovered, according to the present invention, that heat shock protein may be combined with target antigen and used to induce an immune response which includes a cytotoxic cellular component, i.e., a cellular response.